Invalidate the bigger rect if one rect contains the other in LayoutObject::fullyInvalidateRect()

third_party/WebKit/Source/core/layout/LayoutObject.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2000 Dirk Mueller (mueller@kde.org)
  *           (C) 2004 Allan Sandfeld Jensen (kde@carewolf.com)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2011 Apple Inc. All rights reserved.
  * Copyright (C) 2009 Google Inc. All rights reserved.
  * Copyright (C) 2009 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  *
  * This library is free software; you can redistribute it and/or
@@ skipping 1561 matching lines @@
         LayoutRect invalidationRect(newBounds.x(), oldBounds.maxY(), newBounds.width(), deltaBottom);
         adjustInvalidationRectForCompositedScrolling(invalidationRect, paintInvalidationContainer);
         invalidatePaintUsingContainer(paintInvalidationContainer, invalidationRect, PaintInvalidationIncremental);
     } else if (deltaBottom < 0) {
         LayoutRect invalidationRect(oldBounds.x(), newBounds.maxY(), oldBounds.width(), -deltaBottom);
         adjustInvalidationRectForCompositedScrolling(invalidationRect, paintInvalidationContainer);
         invalidatePaintUsingContainer(paintInvalidationContainer, invalidationRect, PaintInvalidationIncremental);
     }
 }
 
 void LayoutObject::fullyInvalidatePaint(const LayoutBoxModelObject& paintInvalidationContainer, PaintInvalidationReason invalidationReason, const LayoutRect& oldBounds, const LayoutRect& newBounds)

[pdr., 2016/04/12 03:01:22]

This logic took me a while to reason through. It's correct, but I wonder if we
could make it easier to understand without affecting the compiled result? Maybe
something like the following where we don't re-use invalidationRect:

// The following logic avoids invalidating twice if one set of bounds contains
the other.
if (!oldBounds.contains(newBounds)) {
    LayoutRect invalidation = newBounds;
    adjustInvalidationRectForCompositedScrolling(invalidation,
paintInvalidationContainer);
    invalidatePaintUsingContainer(paintInvalidationContainer, invalidation,
invalidationReason);

    // Early out when the old bounds have already been invalidated.
    if (newBounds.contains(oldBounds))
       return;
}
LayoutRect invalidation = oldBounds;
adjustInvalidationRectForCompositedScrolling(invalidation,
paintInvalidationContainer);
invalidatePaintUsingContainer(paintInvalidationContainer, invalidation,
invalidationReason);

[Xianzhu, 2016/04/12 16:47:50]

Done (except that oldBounds and newBounds inversed to keep the sequence the same
as before if both need invalidation).

 {
-    // Otherwise do full paint invalidation.
     LayoutRect invalidationRect = oldBounds;
+    bool oneRectContainsTheOther = true;
+    if (newBounds.contains(oldBounds))
+        invalidationRect = newBounds;
+    else if (!oldBounds.contains(newBounds))
+        oneRectContainsTheOther = false;
+
     adjustInvalidationRectForCompositedScrolling(invalidationRect, paintInvalidationContainer);
     invalidatePaintUsingContainer(paintInvalidationContainer, invalidationRect, invalidationReason);
-    if (newBounds != oldBounds) {
+    if (!oneRectContainsTheOther) {
         invalidationRect = newBounds;
         adjustInvalidationRectForCompositedScrolling(invalidationRect, paintInvalidationContainer);
         invalidatePaintUsingContainer(paintInvalidationContainer, invalidationRect, invalidationReason);
     }
 }
 
 void LayoutObject::invalidatePaintForOverflow()
 {
 }
 
@@ skipping 2080 matching lines @@
         const blink::LayoutObject* root = object1;
         while (root->parent())
             root = root->parent();
         root->showLayoutTreeAndMark(object1, "*", object2, "-", 0);
     } else {
         fprintf(stderr, "Cannot showLayoutTree. Root is (nil)\n");
     }
 }
 
 #endif